U.S. Pat. No. 3,275,626 describes a process for converting a penicillin S-oxide into a desacetoxycephalosporin by heating said penicillin S-oxide at a temperature between 100.degree. and 175.degree.C under acid conditions. Modifications in the above-mentioned process are described in British patents 1,204,394 and 1,204,972 and in Belgian patents 745,845, 747,382 and 753,765.
Still according to the literature, good yields of cephalosporin compounds can be obtained by employing, as acid catalysts, hydrocarbon sulfonic acids or phosphoric acids (Belgian patent 747,118) optionally in the presence of a nitrogenous base (Belgian patent 747,119), or a O-mono substituted or 0,0-diaryl substituted phosphoric acid, or its salts with nitrogenous bases (Belgian patent 747,120).
According to Belgian patent 763,104, the penicillin S-oxides can be arranged into the corresponding desacetoxycephalosporins by heating in the presence of a large excess of an organic, nitrogenous base and of an excess of a silicon compound having a silicon-halogen bond.
Thus, the methods of the prior art envisage the use of acid catalysts or the presence, at the same time, of an organic base and of a halogenated silicon derivative. According to these methods, the reaction takes place under rather strong conditions. Particularly, the S-oxides of the penicillins are subjected to prolonged heating at high temperatures in an acidic medium or, anyway, in the presence of large amounts of very reactive products. Under these conditions, both degradation of the penicillin nucleus and formation of undesired by-products occur. Actually, in order to reduce the formation of said by-products, it is suggested, according to the literature, that the reaction time should not be prolonged (U.S. Pat. No. 3,275,626), that thigh temperatures should be avoided (Belgian patent 763,104) and that the following conditions should concurrently be satisfied: careful choice of the reaction solvent, careful choice of the acid catalyst and careful choice of both the temperature and the reaction time (Belgian patent No. 747,118). Nevertheless, by operating according to the known methods a certain degradation of the penam nucleus cannot be avoided.